1. Field of the Invention
This invention relates to an apparatus for feeding a workpiece in a machine tool, particularly in a sewing machine, comprising a main conveyor for longitudinally conveying the workpiece in a feeding direction and an auxiliary conveyor for transversely conveying the workpiece to align the same, which auxiliary conveyor comprises a conveying mechanism, which precedes or succeeds the main conveyor and is engageable with the workpiece as it is guided along a guideway and comprises conveying elements which are adapted to be driven to move transversely to the feeding direction.
2. Description of the Prior Art
It should be possible to feed a workpiece to be processed not only along a straight path but also along an arcuate path and to advance the workpiece in a direction which is parallel to an edge or hem. It is known to accomplish this in that machine tools, particularly sewing machines, are provided with a feeding apparatus, which is composed of a main conveyor and an auxiliary conveyor. The main conveyor moves the workpiece along a straight line in the feeding direction and the auxiliary conveyors imparts to the workpiece in case of need a transverse movement, which is normal to the feeding direction, so that the workpiece can be fed along a straight or an arcuate path or in a direction which is parallel to an edge in dependence on whether or not tile auxiliary conveyor is operated and on its direction of conveyance. As is apparent from EP-B 0 383 045 it is known to provide such apparatuses with auxiliary conveyors which comprise a conveying mechanism which is engageable with the workpiece and comprises a conveyor chain, which revolves transversely to the feeding direction and carries rotatable rolling elements. When the conveyor chain engages the workpiece said rolling elements can roll on the workpiece in the feeding direction and thus enable a feeding of the workpiece along a straight line. When the conveyor chain is being driven the rolling elements constitute coupling means acting on the workpiece to move it transversely to the feeding direction. But in that case there are only point contacts between the rolling elements and the workpiece and the transverse movement of the rolling elements must be superposed on the rolling movement in the feeding direction. The latter fact often gives rise to difficulties in the transverse conveyance of the workpiece to align the same. Such difficulties are particularly undesirable in the feeding of workpieces soft, compressible workpieces, such as textile products. Besides, the rolling elements must be non-displaceably mounted on the chain but must freely be rotatable. These requirements give rise to a high structural expenditure and high maintenance expenditure.
CH-A-650,293 discloses tentering means for use in sewing machines for processing tubular workpieces. Said tentering means comprise two rotatable tentering members for tentering the workpiece and aligning means, which are associated with the tentering members and serve for the proper alignment of the edges of the workpiece for the sewing operation. The aligning means are inserted in the tentering members or in separate roll-like bearing members. The aligning means consist of gears, which extend in planes which are axial with respect to the axes of rotation of the tentering members or bearing members. Said gears are adapted to be driven by a worm gear independently of the associated tentering or bearing member so that the workpiece which has been fitted on the tentering members can be aligned even during a rotation of the tentering member in that the workpiece is displaced in the axial direction of the tentering members by said gears. But in that case there is also only a point contact between the workpiece and the aligning member and the aligning members cannot engage and guide the workpiece directly at its edges so that such aligning means cannot effectively be used to align two-dimensional workpieces by a transverse conveyance.